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A lot has been made of the possibility that the loss of Arctic sea ice could make mid-latitude weather weirder by causing wriggling meanders in the jet stream. One possible manifestation of that is bitter cold snaps in winter, as Arctic air slides south along with the jet stream boundary. There is a correlation between cold mid-latitude winters and low sea ice cover in the Arctic. But does the one really cause the other?

The possible relationship between a warming Arctic and changing behavior of the jet stream is still a matter of real scientific debate. For a number of reasons, it’s a difficult question to resolve. In this case, a team led by the University of Exeter’s Russell Blackport tried to disentangle the chain of events with a clever analysis.

Checking causality

Ultimately, the question is whether shrinking sea ice allows the ocean to warm the atmosphere, or whether the warm air forms separately and then melts the sea ice. The researchers used a pair of climate models and global maps of observed weather; the measurement gaps were filled in by simulated physics. First, the team categorized each winter in North America and Asia based on two measures: cooler or warmer mid-latitude temperatures and lower or higher Arctic sea ice. As in other studies, they found a correlation between the two.

They then turned to calculating the flow of heat between the Arctic atmosphere and ocean, categorizing winters dominated by heat moving into the atmosphere or heat moving into the ocean. If lower sea ice coverage was responsible for the cold mid-latitude winters, you’d expect to see heat moving from the ocean into the atmosphere (and bullying the jet stream) in those years. But instead, they saw the opposite—low sea ice winters were associated with heat coming in the atmosphere that would cause the sea ice to melt.

The researchers did the same thing on shorter timescales, looking to see what came first. They found that the mid-latitude cold weather—and movement of heat from the atmosphere into the ocean—was present about a month before drops in sea ice extent. One month after, they could see heat moving from the newly exposed ocean into the atmosphere, but the cold weather in the mid-latitudes had already ended.

A single cause

In other words, unusual atmospheric circulation patterns would start the wiggle in the jet stream, which both brings cold air south to the mid-latitudes and warm air north to melt sea ice. So the correlation between low sea ice coverage and cold mid-latitude winters is actually because they are both being caused by the same thing.

For a third way of checking this, the researchers ran climate model simulations where Arctic sea ice coverage was set to be smaller than it is today, just without any further greenhouse gas increases and global warming. The idea was to isolate the effect of the sea ice itself. In the simulation, there was still a correlation between low sea ice winters and cold in the mid-latitudes, but the mid-latitudes didn’t get any colder than they were with modern, greater sea ice coverage—supporting the overall conclusion.

This doesn’t mean there’s no connection between global warming and a wriggly jet stream. That research will continue. It does, however, mean that suggestions of a link between shrinking Arctic sea ice and wilder mid-latitude winters were off the mark.

As fascinating as this is, you cannot underestimate the size of the opportunity missed by not referencing The Day After Tomorrow. That’s like writing an article about DNA half life being too short to extract dinosaur DNA from a mosquito in amber and not mentioning Jurassic Park!

The real shame is all the "it's cold here right now therefore global warming is a hoax" nonsense we have to endure every time the jet stream dips farther south.

That's only in winter for whatever hemisphere in which they are located, and of course those in the other one experiencing summer use the "it's hot" meme to deliver the same denialist slant in their tag-team idiocy.

An article that came out a few months ago, which I can't find now gave a reason for cold arctic air dropping into the US Midwest. If I recall correctly: a warmer pacific ocean causes warmed air above to rush in and be deflected by the Rocky Mountains up into the jet stream and destabilizing it. The jet stream would normally be encircling and trapping the cold arctic air, known as the polar vortex. If I recall it was NASA which had released a graphic animation of the air currents and the disrupted vortex. Funny how a group of scientists, having worked on a project will make a press release when their ideas are already obsolete. Happens regularly.

It does, however, mean that suggestions of a link between shrinking Arctic sea ice and wilder mid-latitude winters were off the mark.

Interesting article. I would suggest that we say "suggestions of a causal link" in the quote above. As the researchers have affirmed and you've reported there is a convincing correlative link that follows from a causal link between unusual atmospheric circulation and each of the two correlatively linked events, diminishing sea ice and wiggles in the Jet Stream.

An article that came out a few months ago, which I can't find now gave a reason for cold arctic air dropping into the US Midwest. If I recall correctly: a warmer pacific ocean causes warmed air above to rush in and be deflected by the Rocky Mountains up into the jet stream and destabilizing it. The jet stream would normally be encircling and trapping the cold arctic air, known as the polar vortex. If I recall it was NASA which had released a graphic animation of the air currents and the disrupted vortex. Funny how a group of scientists, having worked on a project will make a press release when their ideas are already obsolete. Happens regularly.

And how does that research discredit the research on sea ice in this article? You cite an article discussing one specific example of arctic air intrusion in one specific area (Midwest). This article attempts to explain it on a broader scale over the entire northern hemisphere. Weather can be caused by a number of factors, and what I’m reading here doesn’t make either piece of research of this phenomena obsolete.

In other words, unusual atmospheric circulation patterns would start the wiggle in the jet stream, which both brings cold air south to the mid-latitudes and warm air north to melt sea ice. So the correlation between low sea ice coverage and cold mid-latitude winters is actually because they are both being caused by the same thing.

Is this saying that we do not know why the jet stream sometimes dips? That when it does, it produces both increased warmth to the north and cold to the south (which we knew already surely).

But the new point is that it now seems to have been shown that its not a case of the increased warmth or cold causing the jet stream to dip?

An article that came out a few months ago, which I can't find now gave a reason for cold arctic air dropping into the US Midwest. If I recall correctly: a warmer pacific ocean causes warmed air above to rush in and be deflected by the Rocky Mountains up into the jet stream and destabilizing it. The jet stream would normally be encircling and trapping the cold arctic air, known as the polar vortex. If I recall it was NASA which had released a graphic animation of the air currents and the disrupted vortex. Funny how a group of scientists, having worked on a project will make a press release when their ideas are already obsolete. Happens regularly.

And how does that research discredit the research on sea ice in this article? You cite an article discussing one specific example of arctic air intrusion in one specific area (Midwest). This article attempts to explain it on a broader scale over the entire northern hemisphere. Weather can be caused by a number of factors, and what I’m reading here doesn’t make either piece of research of this phenomena obsolete.

I don’t find the article super succinct or concise. I do know we can research climate change until we’re extinct and are. Trying to understand a reality that has never existed before and is therefore unlike anything from the past. And of course the solutions to the problem do exist and the failures addressing it political.